1. Field of the Invention
The invention relates to a method for determining the spatial concentration of the various components of a mixture, in particular of a gas mixture in a combustion chamber, of a motor for example.
2. Description of the Prior Art
A method of the type mentioned above is known from internal combustion engines for example; several ports are hereby provided in the combustion chamber, in a cylinder e.g., whereas the spatial concentration of the different components in the fuel-air mixture including potential residual gases is detected by means of optical devices, e.g. by means of mirrors. Knowledge of the local concentration of the different components of such a mixture, for example of a mixture of fuel, oxygen, nitrogen and residual gas is needed for the optimization of combustion in the combustion chamber. Since the state of the art requires a plurality of portsxe2x80x94at least two ports for the spatial determination of the concentration of the gas mixture are neededxe2x80x94construction implies quite complicated measures to make such a determination possible. So-called xe2x80x9cglass motorsxe2x80x9d are also known, which also offer the possibility to optically record the concentration of different gases in a gas mixture in the combustion chamber.
All these known methods and devices have as a common drawback not only the fact that their construction is complicated but also, and this is much more important, that the real flow and combustion conditions are falsified since the creation of the optical port often involves great changes in the geometry of the combustion chamber. Changes in the combustion chamber geometry always affect however the processes of combustion, too. Therefore, the combustion chamber should be altered as little as possible by the optical port on one side. On the other side however, measurements should be made possible and should be as detailed as possible, as e.g. local detailed measurements of gas concentrations.
By using only one aperture, optical measurements could also be made on hardly changed series production engines by removing for example the pressure absorber or the spark plug and by replacing it by an optical port.
The object of the present invention is therefore to provide a method and a device with the help of which the expenditure needed to determine the spatial concentration of the various components of a gas mixture in a space, in particular in a combustion chamber, may be minimized, but that still yields accurate results.
According to the present invention, a laser beam is hereby directed through one unique aperture arranged in the combustion chamber, whereas the laser beam brings particles of the mixture situated on one line to radiate, whereas the light emitted by the particles is then passed backward through the same aperture and is focused on a light-sensitive surface (e.g. on an intensified CCD-camera) to form an image via a specially darkened lens. The particles are so strongly excited by the laser beam that they emit photons. The photons bring the light-sensitive surface to radiate. The brightness of the particles and the size of the radiant surface on the light-sensitive surface permits to determine locally and separately the concentration of the particles along the line defined by the laser by means of an array photodetector (e.g. an intensified CCD-camera).
The important point is that the emissions induced on one line are recorded backward as photons so that only one optical port is needed, whereas the local course of concentration may still be determined.
It is well known that by choosing or acquiring certain optical parameters (such as the wave length and the polarization of the exciting laser, the wave lengths of the light radiated by the particles, the analysis of the polarization or the duration of radiation) it is possible to identify the individual components of a particle mixture and to also determine separately the concentration of individual components by adequate measures (e.g. filtration). Radiating substances (tracers, e.g. colours) may be added to the components of the gas mixture (e.g. air, fuel or combustion gas) in order to deduce the concentration of the corresponding components from the radiation of these additives.
The method foots on the cognition that a laser emits light with a specific wave length that brings the particles of the gas mixture to radiate. The wave length of the light emitted by the particles upon excitation through the laser depends on the type of the particles, whether the particles involved are oxygen molecules, fuel molecules, nitrogen molecules or tracer molecules added to substances.
In order to determine the concentration of individual particles or molecules in the combustion chamber at different places, the reasoning made with reference to a projection lens is that particles or objects in general illuminate on the focal plane a surface that gets bigger in size as they are located farther away from the plane of object. Defining z as the distance between the focal plane and the plane of object (z=0 for the plane of object), the points radiating in the focal plane provide circular surfaces that get bigger in size the farther they are from the plane of object. Radiating points located at different distances z from the plane of object on the line defined by the laser hence provide circular surfaces of different size in the focal plane.
To limit backward the light beam emitted by the particles is particularly important. By masking centrally the beam of rays emerging from one source, the surface projected in the focal plane is no longer circular but is a circular ring having a radius R and a thickness xcex94R. The thickness of the circular ring is getting smaller when the beam is increasingly limited in diameter. In this arrangement, the radiation occasioned by the laser in a spatial area [z1, z2] is imaged on the focal plane in a radial area [R1, R2]. The number of photons emitted in the spatial area [z1, z2] may be determined from the integration of the radiation intensity recorded in the radial area [R1, R2]. The number of emitted photons permits to determine the concentration of the particles according to well known procedures, e.g. Raman scattering.
By luminating one line in the combustion chamber by means of a laser, a system of concentric circular rings is created in the focal plane, whereas the light recorded at different radial intervals may be allocated to different sources on the laser line. The local concentration of individual components of a gas mixture in a combustion chamber is thus possible, since the distance separating the concentration of particles from the plane of object, and hence from the cylinder wall, can be determined.
A semireflecting mirror may possibly be arranged in the beam path of the laser. By having a mirror arranged in the beam path of the laser, it is possible to introduce the laser beam through the same port in the cylinder through which the light emitted by the particles is coming out. The important fact is that, thanks to this method according to the invention, only one port into the combustion chamber is needed to send the laser through this port into the combustion chamber and to receive the light emitted by the particles.
The array to carry out the previously described method is characterized by a laser, a mirror arranged in the beam path of the laser as well as by a lens arranged in the beam path of the light emitted by the particles, a display being arranged behind said lens. The lens is hereby opaquely covered on its centre in order to achieve an increased selectivity.
The invention will be explained more explicitly in the following with the help of the drawing illustrating an example thereof.